Does anyone monitor AIS (Ship and Vessel Tracking?)

[abcd567]

@SweetPea11

How was -20 determined?

Few days ago on a spare microSD card, I wrote the image from the site suggested by @geckoVN.

@geckoVN

I’ve just been through the same process with an AIS receiver. The offset with that is opposite sign to bring the error to zero

https://www.sarcnet.org/ais-receiver.html

 

That image has facility to calibrate ppm. I ran that and it gave me a figure of 20.

QUOTE:

Calibrate your AIS Receiver

The operating frequency of the USB RTL-SDR Dongle’s internal Temperature Controlled Crystal Oscillator (TCXO) may not be precisely on frequency, depending on its quality and other factors. However, you can use the RPi clock to calibrate the RTL-AIS service to account for any frequency offset. Note: The frequency offset is measured in Parts Per Million (PPM). Note: For 1PPM RTL-SDRs this step is hardly necessary as the frequency would only be off by +/- 162Hz.

Do the following on the Raspberry Pi:

1. Login:

2. Type: pi

3. Type: Your password

4. Stop the RTL AIS service and run the RTL test

5. Type: sudo systemctl stop rtl_ais.service

6. Type: rtl_test -p60

7. Wait until the cumulative error value (in PPM) remains more-or-less the same for three consecutive minutes

8. Note the last cumulative error value (in PPM).

 

EDIT:

The ppm test can be done on any RPi running RaspberryPi OS image or Piaware SD card image by following method:

sudo apt install rtl-sdr 

sudo systemctl stop piaware dump1090-fa readsb 

rtl_test -p60